The invention described herein relates generally to an air driven centrifuge and more particularly to an improved apparatus for decelerating an air driven centrifuge rotor and for stabilizing such rotor as its speed reduces.
In order to separate certain fluid mixtures, very high speeds of rotation are often required. For example, separation of proteins, viruses and various clinical specimens require extremely high speeds of centrifugation in order to separate fractions thereof within reasonable time spans. It has been found that extremely high rotational speeds (such as 150,000 R.P.M. to 200,000 R.P.M.) can be attained by rotating a centrifuge rotor on a cushion of air with pressurized air streams. An example of such an air driven centrifuge is illustrated in U.S. Pat. No. 3,456,875 issued to George N. Hein on July 22, 1969.
Because air driven centrifuge rotors are supported on a substantially friction-free cushion of air it is difficult to design an air delivery system that will make the rotor come to a gradual, complete stop. While great pains in design can be taken to hold any rotational effect due to the stopping air stream to a minimum, it is impossible to completely eliminate any rotational effect. There is always a certain amount of "windmilling" by the supporting or holding air stream across the turbine flutes of such a rotor.
In addition, the design of a rotor, or the loading of the sample therein, always introduces certain parameters which create critical speeds at which the rotor will precess, wobble or vibrate excessively while decelerating. These critical speeds are usually relatively low rotational speeds and the precession and/or wobbling can become so great as to cause the sample to be remixed or to cause the rotor to come into contact with the sidewalls of its seat thereby causing it to jump from its rotational axis and thrash around within the centrifuge chamber. The present invention overcomes these problems.